I would like to know the correct units to make a SNIR computation.

I am using the following formula:

$$ \text{SNIR} = \frac{1}{\frac{1}{\text{SNR}} + \frac{1}{\text{CIR}}} $$

I have SNR in dB and CIR in dBm.

Shall I convert SNR to dBm to get the SNIR in dBm, or the CIR to dB to get the SNIR in dB, or there is no need to make the units change?.

I want to use the SNIR to compute a BER which is $\approx \frac{1}{4\textrm{SNR}}$


  • $\begingroup$ Can you define CIR? $\endgroup$ – random_dsp_guy Apr 18 '18 at 19:41
  • $\begingroup$ @Seth CIR is the Carrier to Interference Ratio. I have obtained it by taking out the Interfernce in dBm to the received power in dBm. $\endgroup$ – pablo Apr 18 '18 at 19:44
  • $\begingroup$ Hint: I have no idea where you got your formula from but try rewriting it as $$\frac{1}{SNIR} = \frac{1}{SNR}+\frac{1}{CIR}$$ and see if that suggests the way to proceed further. $\endgroup$ – Dilip Sarwate Apr 18 '18 at 20:04

You'll have to convert back into linear units before you can evaluate the SINR formula.

${\textrm{SNR}_{linear}=10^{\big(\frac{\textrm{SNR}_{dB}}{10}\big)}}$ and likewise for CIR...

${\textrm{SINR}_{dB} = 10 \log_{10}(\frac{1}{\frac{1}{\textrm{SNR}}+\frac{1}{CIR}}})$

${BER = \frac{1}{4{\textrm{SINR}}_{linear}}}$


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